The compressors of jet engines include a number of axially spaced banks or rows of fixed stator vanes which are positioned between rows of rotatable rotor blades. Each stator vane is mounted to a platform which is carried in a circumferential T-shaped slot, dovetail slot or similar structure formed in the compressor casing. In many compressors, each separate stator vane has its own platform and these stator vane platforms abut one another within each row around the circumference of the compressor.
In order to maximize efficiency, it is important to maintain the flow of air rearwardly or downstream through the compressor and limit backflow of air in the opposite, upstream direction. One area where an unwanted backflow of air has been produced is at the connection between the stator vane platforms and the compressor casing, particularly in the high pressure areas of the compressor. It has been found that a backflow of air develops between the stator vane platforms and the T-shaped or dovetail slots in the compressor casing within which they are mounted. Additionally, the abutting edges of adjacent stator vane platforms within each circumferential bank or row of stator vanes form a path along which high pressure air can leak and create a backflow in the upstream direction.
One approach in the prior art to overcome this backflow problem has been to increase the arc length of the stator vane platforms so that a number of stator vanes can be mounted to a single platform. This reduces the number of joints between abutting stator vane platforms within each row of stator vanes and thus lessens the leakage problem found in prior art compressors which employ a separate platform for each stator vane.
Although larger stator vane platforms reduce the backflow problem, several other problems are created. The tolerance between the dovetail or T-shaped slots in the compressor casing and the stator vane platforms must be kept to a minimum for two reasons. First, the backflow of air in an upstream direction along a path between the stator vane platforms and compressor casing must be limited to maximize the efficiency of the compressor. Secondly, the appropriate clearance must be maintained between the stator vane platforms and the tips of the rotor blades.
When the arc length of the stator vane platforms is increased, they become more susceptible to warpage, and, manufacturing tolerances also increase. This makes assembly of the larger stator vane platforms within the circumferential dovetail or T-shaped slots in the compressor casing a very difficult maintenance procedure. Assuming stator vane platforms having a large arc length can be forced into a slot in the compressor casing, their removal is even more difficult due to oxidation of the such surfaces during operation of the jet engine at high temperature.
On the other hand, if the dimensions of the T-shaped or dovetail slots in the compressor casing are increased to aid in assembly and disassembly, leakage of air in the upstream direction between the stator vane platforms and compressor casing increases. Additionally, the required spacing between the stator vane platforms and rotor blades cannot be maintained.